The prior art shows many years of concern over the production of vibration-resistant fastener combinations. Simply stated, one approach involves the use of additional elements such as lock washers, cotter pins and glue bonds which are separate and distinct from the male and female elements of the fastener combination. The assembly of such elements adds significant cost to a high production application. Another approach involves the formation of shallow angled surfaces in the male and female thread forms which telescopically engage under axial tension to produce a self-locking effect. This approach has the negative effect of being very difficult and expensive to manufacture because of the close tolerances required. Other approaches such as deforming the nut after application are also disclosed in the prior art.
I have discovered that the key to a vibration-resistant self-locking fastener combination lies in the realization of firm radial contact between the male and female thread forms such that all lateral movement is constrained under vibration conditions. By eliminating the possibility for lateral shifting or relative movement between the thread forms, the high friction condition is maintained and an unwinding of the threads under axial tension conditions is eliminated. I have embodied this concept in a free-running fastener combination as disclosed in my co-pending application for U.S. Patent Ser. No. 755,437, filed Dec. 29, 1976 as a continuation of U.S. Ser. No. 620,566, filed Oct. 8, 1975, now abandoned. I have now found that I can apply this concept to a prevailing torque fastener combination.